Magnetic tape provides a means for physically storing data. As an archival medium, tape often comprises the only copy of the data. The tape is typically made as thin as practically possible to maximize the length of a tape stored on a tape reel and thereby maximize the amount of data that can be stored on the tape contained in a single cartridge. A tape drive is used to store and retrieve data with respect to the magnetic tape. An example of a tape drive is the IBM TotalStorage Enterprise Tape Drive 3592 manufactured by IBM Corporation. Tape drives are typically used in combination with an automated data storage library. For example, the IBM TotalStorage Enterprise Tape Library 3494 manufactured by IBM Corporation is an automated data storage library that may include one or more tape drives and data storage media for storing data with respect to the tape drives.
FIGS. 1 and 2 illustrate an exemplary configuration of a known write mechanism of a tape drive employing a “H” configuration of write drivers in the form of FET devices M1-M4 for driving a write current IW through a write head L1. Under normal write conditions, an AC control signal IN and an AC control signal NOT_IN are applied to respective inverters to logic inverters A1 and A2 to facilitate a bi-directional cyclic flow of a write current IW through write head L1. Specifically, in a first cycle phase with AC control signal IN being a logic low and AC control signal NOT_IN being a logic high, FETs M2 and M3 are conductive and FETs M1 and M4 are nonconductive whereby write current IW flows from FET M3 through write head L1 to FET M2. Conversely, in a second cycle phase with AC control signal IN being a logic high and AC control signal NOT_IN being a logic low, FETs M1 and M4 are conductive and FETs M2 and M3 are nonconductive whereby write current IW flows from FET M4 through write head L1 to FET M1.
For the voltage mode write driver circuit of FIG. 1, a magnitude of write current IW is dependent upon a voltage source VS and a pair of resistors R1 and R2 in view of the design of FETs M1-M4 having a low drain-source voltage drop when in a conductive state, and for the current mode write driver circuit of FIG. 2, the magnitude of write current IW is dependent upon a current source IS in view of the design of FETs M1-M4 having a low drain-source voltage drop when in a conductive state. Nonetheless, for both write driver circuits, the size of FETs M1-M4 must be selected for the maximum magnitude of write current IW required for all applications. However, the AC power of AC control signals IN and NOT_IN are affected by the size of FETs M1-M4, as represented by a Z factor equal to a width of a FET divided by a length of a FET, and by the switching frequency at which AC control signals IN and NOT_IN are changing between logic states.
As related to the size of FETs M1-M4, each FET M1-M4 has a respective capacitance C11-C42 that must be charged when switching a FET from being nonconductive to conductive, and must be discharged when switching a FET from being conductive to nonconductive. Each capacitance C11-C42 is proportional to the size of FETs M1-M4. As a result, the total AC power of AC control signals IN and NOT_IN increases with any increase in the size of FETs M1-M4. Consequently, the storage industry is constantly striving to improve upon techniques for maximizing the magnitude of write current IW required for all applications while minimizing the AC power needed to operate the write driver circuit.